Well Done – Material Handling by AS-i

By means of the monitored and time-limited suppression of protective functions, the productivity of automated systems can be increased significantly. With the muting technology developed by Leuze electronic for the AS-i Safety Monitor, this can now easily be achieved with AS-Interface Safety at Work up to category 4 acc. to EN 954-1 or Pl e acc. to EN ISO 13849-1. This is clearly demonstrated in an application at NORD Gear (NORD DRIVESYSTEMS), realized by system manufacturer Daifuku in collaboration with UCS and Leuze electronic.

For the implementation of a Sorting Transfer Vehicle (STV) application at NORD DRIVESYSTEMS, UCS, together with system manufacturer Daifuku, chose to realize the safety circuit on the basis of AS-Interface. The decisive factor here was the muting function integrated in the AS-i Safety Monitor from Leuze electronic (see box 1 "AS-i", box 2 "NORD DRIVESYSTEMS", box 3 "Daifuku", box 4 "UCS", box 5 "Leuze electronic", box 6 "Muting"). Christian Fornée, project leader and person responsible for software development at UCS says: "We implement many AS-i applications, primarily in the area of conveyor systems. Frequency-controlled motors are increasingly used in these systems. In this regard, AS-i is the more economical and functionally sufficient variant of PROFIBUS, because often only two speeds with reversal of rotational direction are required."

System design

The complete application at NORD DRIVESYSTEMS includes five E-STOP areas—three based on AS-i Safety at Work and two conventional areas that utilize hard-wired transducers. A typical E-STOP area with muting at NORD DRIVESYSTEMS consists of:

• 2 x AS-i Safety Monitors

• 9x Multiple Light Beam Safety Devices

• 9x muting sensors

• 3x AS-i E-Stop buttons

Each E-STOP area acts on its respective region of interest and on the STV loop. Located to the left and right of the safety light barrier are parking spaces on the chain and roller conveyors. The STV loop is fenced-in and can only be entered for service purposes through an entry door provided for this purpose. This was realized with a key concept in such a way that even after entering the danger area, the loop can again be put under voltage. This gives the maintenance employee opportunity to operate the vehicles in set-up mode.

Operating sequence and requirements

Euro pallets and wire-mesh boxes are moved on the roller conveyors. The STVs pass corresponding loading device to the conveyor system. Due to the tight dimensioning of the system construction, the main problem was implementing a smooth, automated transfer from the STV to the conveyor system via muting areas.

The lifting equipment comes to a standstill in front of the hard guard: it cannot move in immediately, as a parking space would otherwise be lost. There is very little space in front of the hard guard, and the lifting equipment stops just 12 cm in front of the protective field of the safety light barrier used for monitoring the transfer area. During this waiting phase, both muting sensors (Light Beam Devices) must not be damped, as a muting error would otherwise occur with this muting operating mode, "parallel muting". Therefore, due to the AS-i query cycle, the muting Light Beam Devices must be arranged with a slight offset. Because the lifting equipment moves in at a speed of 0.5 m/s, it must also be ensured that the muting sequence is initiated in good time while the protective field is being passed through. A major challenge here was the offset switching of the muting sensors, as not all lifting equipment is always parallel to the conveyor system.

AS-i muting solution in detail

After many test settings, UCS decided to realize parallel muting via a sensor signal and a machine signal. As a result, lifting equipment that is not parallel is still able to pass through the protective grid. Commenting on the principle structure, Christian Fornée says: "AS-i Safety was used here for the first time. We chose this because we are evaluating 20 Multiple Light Beam Safety Devices for monitoring the transfer areas and eight E-Stop buttons via the safe AS-i bus. The protective sensors with AS-i connection are a very economical solution if the muting functionality is moved to the AS-i Safety Monitor. The amount of wiring required is then very low compared to conventional wiring."

With Leuze electronic, UCS has chosen a competent partner who can supply precisely the right solution for the described muting application with the ASM AS-i Safety Monitor (see box 7 "ASM"). Because Safety Monitor models ASM1E-m and ASM2E-m are equipped with selectable muting functions. As a result, they facilitate the time-monitored bridging of the protective device based on AS-i during material transport, without any process interruptions. The entire muting configuration is performed easily and quickly via the asimon configuration and diagnostics software (see box 8 "asimon").

Economical up to safety category 4

The integration of the muting function in the AS-i Safety Monitor results in a particularly economical and flexible automation solution through AS-Interface, as the sensor peripherals of the system required for the muting evaluation—the muting and safety sensor—can be queried directly via AS-Interface and evaluated by the AS-i Safety Monitor.

The main cost advantage here is in the possible realization of multiple muting areas with just one AS-i Safety Monitor. To accomplish this in the past, each protective sensor needed to be provided with the muting function or a separate muting controller was necessary for each muting area as a built-in switching cabinet device.

score

With support from UCS and Leuze electronic, Daifuku was able to realize a custom muting solution for NORD DRIVESYSTEMS on the basis of AS-i. All drives in the application at NORD DRIVESYSTEMS are equipped with the company's own drive motors with decentral inverter technology (SK 200E) with AS-i connection. The result is a very economical solution. The good cooperation with Leuze electronic allowed the entire project to be completed quickly, economically and smoothly.